The "narrow" (closed and (?)latticed "windows" lit up both the guard-chambers and the hall. On the square base of the "post" stood the shaft in the form of a palm-tree, as we see in ancient buildings in the east.

Wesley's Commentary
on Ezekiel 40 :15

40:15 And - This verse seems to sum up all the dimensions; this gate, its porch, and thickness of its walls, and so sum the cubits, six in the thickness of the outer wall, eighteen in the three chambers, twenty in the spaces between the chambers, and six cubits in the thickness in the inner wall of the porch.